The present invention relates to a valve position detector which exactly detects a position of a valve during firing in an engine.
When components in a valve operating mechanism are changed in specification, an actual position of a poppet valve is measured to evaluate the components depending on movement characteristics or to investigate followability of the valve to a cam. For measurement, an axial position of the valve or components which move therewith such as a valve spring retainer is detected by a sensor.
However, in a direct-acting type valve operating mechanism, not only an axial end of the valve, but also a valve spring retainer, which is mounted via a cotter, is positioned in a cap-like tappet. In a relatively small engine, there is no space for the sensor around the valve operating mechanism, so it is very difficult to detect position of the valve or valve spring retainer directly. Therefore, a piston and a connecting rod are detached from a cylinder block of the engine, and a non-contacting displacement sensor, such as an approach sensor, is provided just under the valve in the cylinder. By operating the engine on a support, axial displacement of the valve is determined at a valve head.
Such measurement on the support is not the same as actual measurement of the valve during firing of the engine. Combustion pressure in the cylinder or an influence to the valve such as back pressure of an exhaust system, cannot be determined exactly. In such measurement using the approach sensor, detection accuracy is poor.
Instead of a valve operating mechanism by an ordinary cam, various electromagnetic valve drivers are suggested to open and close a valve by magnetic force.
In such a valve drive system, to control opening/closing time of the valve exactly depending on an operating condition of the engine, and to enable feedback control of electric current to an electromagnet for a driving valve, it is indispensable to provide a valve position detector to detect a present position of the valve at high accuracy. Thus, there is a need to provide a high accuracy valve position detector instead of the above close small approach sensor.